Monolithic ICs generally comprise a number of transistors, such as metal-oxide-semiconductor field-effect transistors (MOSFETs), fabricated over a planar substrate, such as a silicon wafer. ICs often include at least one fuse. A fuse is a sacrificial device that may be employed to provide IC overcurrent protection, secure and IC, or otherwise program operation of an IC. A fuse starts with a low resistance and is designed to permanently create a non-conductive path when the current across the device exceeds a certain level.
Some fuse designs employ narrow interconnect metal line. As a high enough current passes through the thin metal line, the metal line melts and creates an open circuit. To have a low program current, the cross-section of the fuse needs to be small compared to other circuit conductors. Another approach leverages electromigration between two metal materials. When two or more conducting metals interface, momentum transfer between conduction electrons and metal ions can be made large where there is a non-uniform metal ion lattice structure. Above a certain current level, atoms move and create voids near the bimetal interface, thus creating an open circuit. For such a fuse architecture, the overlap area between metals and the electromigration properties of the metals determine the fuse program current.
As fuse architectures reliant on electromigration are generally incompatible with efforts to mitigate electromigration for sake of improved device reliability, metal-line based fuse architectures are advantageous. Also, with MOS transistor dimensions scaling from one technology generation to the next, it is desirable to scale down fuse size, as well as fuse program current. However, for interconnect metal line fuse elements, interconnect metal line resistance has trended up over recent IC technology generations. An increase in fuse resistance reduces current through a fuse element at a given supply voltage, making it more difficult to create an open fuse circuit (e.g., requiring a greater fuse program voltage).
Interconnect fuse architectures and associated fabrication techniques capable of lower program currents, and/or smaller fuse areas are therefore advantageous for advanced MOS ICs.